The **E3JK-R4M2** is a popular industrial photoelectric sensor manufactured by Omron (and various compatible brands). It is a **retro-reflective** sensor, meaning it emits light and detects it when it bounces back from a reflector. --- ## 1. Technical Specifications The E3JK-R4M2 is known for its versatility because it operates on both AC and DC voltages and uses a relay output. | Feature | Specification | | :--- | :--- | | **Sensing Method** | Retro-reflective | | **Sensing Distance** | Typically 2 to 5 meters (depending on reflector) | | **Supply Voltage** | 12 to 240 VDC or 24 to 240 VAC | | **Output Type** | Relay Output (SPDT) | | **Contact Rating** | 3A at 250 VAC | | **Light Source** | Infrared LED | | **Response Time** | 30 ms maximum | | **Protection Rating** | IP64 / IP66 (depending on variant) | --- ## 2. Wiring and Internal Components The sensor uses a 5-wire system. Inside the unit, the electronics convert the high-voltage input into low-voltage DC to power the infrared emitter and the receiver circuit. ### Wiring Color Code: * **Brown & Blue:** Power Supply (Non-polarized, can be AC or DC). * **White:** Common (COM) for the relay. * **Black:** Normally Open (NO) contact. * **Gray:** Normally Closed (NC) contact. --- ## 3. Core Electronic Operation The device functions through three main stages: 1. **Emitter Stage:** An Infrared (IR) LED pulses light toward a dedicated reflector (like the E39-R1). 2. **Receiver Stage:** A phototransistor or photodiode waits for the reflected light. It is tuned to the specific frequency of the emitter to avoid interference from ambient sunlight or room lighting. 3. **Output Stage:** When the light beam is broken (interrupted by an object), the internal logic triggers a mechanical **Electromagnetic Relay**. This allows the sensor to switch heavy loads directly without needing an external PLC or transistor buffer. --- ## 4. Key Advantages * **Universal Voltage:** One sensor can be used in almost any power environment (12V battery up to 240V mains). * **Built-in Relay:** Simplifies wiring for simple "on/off" tasks like opening a garage door or stopping a conveyor. * **Long Range:** Retro-reflective sensors cover more distance than diffuse-reflective types.